Polybutene is the polymer formed by the polymerization of a mixture of olefin components having four carbon atoms (C4), derived by the naphtha cracking process, using a Friedel-Craft type catalyst. The number average molecular weight (Mn) is about 300 to 5,000. The C4 residual obtained after extraction of 1,3-butadiene from crude C4 is referred to as “C4 raffinate-1”, which includes paraffins, such as isobutene, n-butane, etc., and olefins, such as 1-butene, 2-butene, isobutene, etc. The isobutene content is approximately 30 to 50 wt. %. The C4 raffinate-1 is primarily used in the preparation of methyl-t-butyl ether (MTBE), which is a gasoline additive to raise the octane number, or polybutene. Isobutene is the most reactive one of the olefin components in the C4 raffinate-1, so the polybutene prepared from isobutene is primarily composed of isobutene units. The polybutene can also be produced from high-purity isobutene or butane-butene raffinate (B-B raffinate) that is a C4 mixture derived by the crude oil refining process.
The viscosity of the polybutene increases with an increase in the molecular weight and ranges from about 4 to 40,000 cSt (centi-stocks). Further, the polybutene is susceptible to pyrolysis at a temperature of 300° C. or above without residue and very soluble to lubricating oils or fuels due to its branched chain having an alkyl structure. Thus, the polybutene can be added to engine oils as an anti-scuff agent or a viscosity index improver, or mixed with fuels in the internal combustion engine for automobile or the like and used as a cleaning agent.
Because polybutene is mainly used in gluing agents, adhesives or insulating oils, high reactivity polybutene has not been favored. In recent years, however, the demands for high reactivity polybutene have risen steadily with the increasing use of the polybutene having polar groups introduced to enhance reactivity as a fuel cleaner or a lubricant additive. Thus, non-reactive polybutene (generally called and referred to as “regular polybutene” in this specification as needed) is used in gluing agents, adhesives, insulating oils, etc., while high reactivity polybutene and midrange reactivity polybutene, capable of having polar groups introduced using reactivity, are mainly used in fuel cleaners or lubricant additives. Most widely used polybutene products produced by introducing polar groups into polybutene are, for example, polyisobutenyl succinic anhydrides (PIBSA) prepared by reacting the terminal double bond of high reactivity polybutene with maleic anhydride in a thermal process, and alkyl phenols (e.g., polybutenyl phenol, etc.) prepared by the Manich reaction of phenols and midrange reactivity polybutene. These polybutene products are advantageously considered as functional polymers. Most of the lubricant additives or fuel cleaners are prepared with the PIBSA used as an intermediate. As the double bonds of the polybutene used in the preparation of PIBSA are positioned towards the end of the polybutene, the PIBSA can be produced with higher yield. But, the yield of PIBSA possibly decreases due to steric hindrance and the resultant lower reactivity in the case that the double bonds are positioned towards the interior of the polybutene and that the more alkyl groups are attached to the double bonds as substituents.
Forming a terminal double bond of a molecule and then terminating the polymerization reaction means the production of a compound that goes against the general theories of chemical reactions. In the preparation of high reactivity polybutene and midrange reactivity polybutene (also called “middle vinylidene polybutene”) that are difficult to produce, the most important factors are the type of the catalyst and the composition of the cocatalyst system selected in the preparation. Other variables, such as the reaction temperature, the strength of the catalyst, etc., can also to be taken into consideration in the preparation process.
Prior to the advent of high reactivity polybutene, regular polybutene, that is, non-reactive polybutene has been used in the preparation of PIBSA. For enhancing the reactivity of the non-reactive polybutene, polybutene is chlorinated with chlorine gas through a chlorination reaction and reacted with maleic anhydride to yield PIBSA. Then, amines are added to the PIBSA to complete the final product. However, this method is not desirable in the economic and environmental aspects, since it costs too much due to expensive equipment used to prevent the corrosion of the reactor and uses a large quantity of a base solution to neutralize the unreacted chlorine gas. In addition, when the final product prepared by adding amines to the PIBSA with the chlorine content raised through the chlorination reaction is used as a fuel additive or the like, it may cause some problems, including corrosion of the internal combustion engine such as automobile engines, etc. and emission of chlorine as an exhaust gas. Accordingly, an improvement has been made towards the method of preparing lubricant additives or fuel cleaners using high reactivity polybutene. Such an advance of using high reactivity polybutenes in the place of non-reactive polybutenes in the lubricant additives or fuel cleaners can be considered as a process improvement that eliminates one step of the reaction and as an eco-friendly method that excludes emission of the toxic chlorine (Cl2) gas.
The non-reactive polybutene is used in a variety of applications, such as gluing agents, adhesives, sealants, lubricant additives, insulating oils, etc., that are required to secure chemical stability (non-reactivity), thermal stability, water barrier property, cohesion, adhesiveness, and so forth. Like this, high reactivity polybutene, midrange reactivity polybutene and non-reactive polybutene are different from one another in their use purpose. It is therefore necessary to control the production of each polybutene in accordance with the demands for the individual polybutenes.
U.S. Pat. Nos. 4,605,808, 5,068,490, 5,191,044, 5,408,018, 5,962,604, and 6,300,444 disclose a preparation method for high reactivity polybutene that has a vinylidene content of at least 70%, more preferably at least 80%, using boron trifluoride or a complex compound of boron trifluoride in the presence of a cocatalyst, such as water, ether, alcohol, etc. U.S. Pat. No. 7,037,999 B2 describes a polybutene having a vinylidene content less than 70% and a tetra-substituted double bond content less than 10%, and its preparation method. Korean Patent No. 10-0787851 mentions the advantages of the tetra-substituted double bonds and an economically effective preparation method for polybutene and specifies a preparation method for midrange reactivity polybutene. Despite that such a number of related patents are given for the high reactivity polybutene, midrange reactivity polybutene and non-reactive polybutene, there can be found no method for selective preparation of a high reactivity polybutene, a midrange reactivity polybutene and a non-reactive polybutene in a single plant.